tcpc: verify that i2c_read for vbus succeeds
tcpc: verify that i2c_read for vbus succeeds

If we cannot contact the TCPC, then we need to assume the safer value
of VBus level (i.e. off)

BRANCH=none
BUG=b:77458917
TEST=yorp C1 still works

Change-Id: I1fc1898a7dc554d050cd3612616531cb74de7261
Signed-off-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/995959
Reviewed-by: Divya S Sasidharan <dba62b20a5027527f6399518550d13252dee26fc@intel.com>
Reviewed-by: Furquan Shaikh <6be5c96c464778f89679b1062a2e0a6af93d2aa5@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec